Tag anti-collision method, reader apparatus and system for RFID systems with multi-packet reception capability

Abstract

Provided is a method of preventing collision between a plurality of RFID tags by an RFID reader. An anti-collision method by a tag reader apparatus in an RFID system including a plurality of RFID tags, includes changing a length of a collision recovery slot in the collision recovery slot which successfully identifies a plurality of tags even though at least two tags simultaneously replied in one slot to cause collision so that data transmission of at least one identified tag is achieved.

What is claimed is: 
     
       1. An anti-collision method by a tag reader apparatus in an RFID system including a plurality of RFID tags, the method comprising:
 changing a length of a collision recovery slot in the collision recovery slot which successfully identifies a plurality of tags even though at least two tags simultaneously replied in one slot to cause collision so that data transmission of at least one identified tag is achieved. 
 
     
     
       2. The anti-collision method of  claim 1 , wherein the changing of the length of a collision recovery slot comprises sequentially transmitting a plurality of ACK commands to the at least one identified tag so that the data transmission of at least one identified tag is sequentially achieved in the collision recovery slot. 
     
     
       3. The anti-collision method of  claim 1 , wherein a success slot to succeed data transmission of the tag, an idle slot where no tags reply, a collision slot where identification fails due to collision, and a collision recovery slot to succeed tag identification even though at least two tags simultaneously replied have different lengths. 
     
     
       4. The anti-collision method of  claim 3 , wherein the length of the collision recovery slot is greater than the length of other slots. 
     
     
       5. The anti-collision method of  claim 3 , wherein a maximum value of a time when a reader waits for a response from a tag in the idle slot is calculated as a time required to transmit one bit of the response from the tag. 
     
     
       6. The anti-collision method of  claim 1 , wherein a frame size is determined so that a system throughput η is maximized by defining a ratio of a time required to identify the tag to time of a slot succeeding tag identification as the system throughput. 
     
     
       7. The anti-collision method of  claim 6 , further comprising:
 calculating a probability of a collision slot based on the number of idle slots and a size of a k-th frame; and 
 estimating the number of tags attempting to be identified in the k-th—the k is an arbitrary natural number—frame by applying the calculated probability of the collision slot to a zero estimation algorithm. 
 
     
     
       8. The anti-collision method of  claim 7 , wherein the number of the tags attempting to be identified in the (k+1)-th frame is calculated by subtracting the number of tags which are successfully identified in the k-th frame from the number of tags attempting to be identified in the k-th frame. 
     
     
       9. The anti-collision method of  claim 8 , wherein a size of the (k+1)-th frame is calculated so that a system throughput indicating a ratio of an average of a slot time succeeding the tag identification to a time average of a unit slot is maximized. 
     
     
       10. The anti-collision method of  claim 9 , wherein a function of the system throughput is 
       
         
           
             
               
                 
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         where, the   represents a probability of the success slot in the (k+1)-th frame, the   represents a probability of the idle slot in the (k+1)-th frame, the   represents a probability of the collision slot in the (k+1)-th frame, the E[D CR ] represents an average time of a collision recovery slot, the D s  represents a time of the success slot, the D i  represents a time of the idle slot, and the D c  represents a time of the collision slot. 
       
     
     
       11. The anti-collision method of  claim 6 , wherein a size of the (k+1)-th frame is calculated to make a partial differential function of the system throughput zero, and an integer form is calculated through a ceiling operator when the frame size is a real number. 
     
     
       12. An RFID tag reader apparatus in an RFID system including a plurality of RFID tags, wherein the RFID tag reader apparatus changes a length of a collision recovery slot in the collision recovery slot which successfully identifies a plurality of tags even though at least two tags simultaneously replied in one slot to cause collision so that data transmission of at least one identified tag is achieved. 
     
     
       13. The RFID tag reader apparatus of  claim 12 , wherein a plurality of ACK commands are sequentially transmitted to the at least one identified tag so that the data transmission of at least one identified tag is sequentially achieved in the collision recovery slot. 
     
     
       14. The RFID tag reader apparatus of  claim 12 , wherein the RFID tag reader apparatus comprises:
 a receiver configured to receive a tag response and data from the tag; 
 a transmitter configured to transmit a Query response command and an ACK command to the tag; and 
 a controller configured to generate the Query response command by determining a length of a slot, to generate a Query command by determining a frame size, and to generate the ACK command based on a response from the tag. 
 
     
     
       15. The RFID tag reader apparatus of  claim 14 , wherein a success slot to succeed data transmission of the tag, an idle slot where no tags reply, a collision slot where identification fails due to collision, and a collision recovery slot to succeed tag identification even though at least two tags simultaneously replied have different lengths. 
     
     
       16. The RFID tag reader apparatus of  claim 15 , wherein the length of the collision recovery slot is greater than the length of other slots. 
     
     
       17. The RFID tag reader apparatus of  claim 15 , wherein a maximum value of a time waiting for a response from a tag in the idle slot is calculated as a time required to transmit one bit of the response from the tag. 
     
     
       18. The RFID tag reader apparatus of  claim 12 , wherein a frame size is determined so that a system throughput η is maximized by defining a ratio of a time required to identify the tag to an occupied time of a slot succeeding tag identification as the system throughput. 
     
     
       19. An RFID system comprising:
 an RFID reader apparatus configured to change a length of a collision recovery slot in the collision recovery slot which successfully identifies a plurality of tags even though at least two tags simultaneously replied in one slot to cause collision so that data transmission of at least one identified tag is achieved; and 
 a plurality of RFID tags configured to transmit a unique identification number of a tag in response to a Query response command from the RFID reader, and to transmit data in response to an ACK command to the RFID reader.